J2ME中使用Canvas制作简单的游戏菜单

package com.j2medev.chapter3; 
import javax.microedition.lcdui.*; 
public class MenuCanvas extends Canvas{ 
//selected变量标记了焦点位置 
private int selected = 0; 
private int preferWidth = -1; 
private int preferHeight = -1; 
public static final int[] OPTIONS = {0,1,2,3}; 
public static final String[] LABELS={"New Game","Setttings","High Scores","Exit"}; 
public MenuCanvas() { 
selected = OPTIONS[0]; 
//计算菜单选项的长度和高度值 
Font f = Font.getDefaultFont(); 
for(int i = 0;i<LABELS.length;i++){ 
int temp = f.stringWidth(LABELS[i]); 
if(temp > preferWidth){ 
preferWidth = temp; 
} 
} 
preferWidth = preferWidth + 2*8; 
preferHeight = f.getHeight()+2*4; 
} 
public void paint(Graphics g){ 
//清除屏幕 
int color = g.getColor(); 
g.setColor(0xFFFFFF); 
g.fillRect(0,0,getWidth(),getHeight()); 
g.setColor(color); 
//计算整个菜单的高度，宽度和（x,y） 
int rectWidth = preferWidth; 
int rectHeight = preferHeight * LABELS.length; 
int x = (getWidth()-rectWidth)/2; 
int y = (getHeight()-rectHeight)/2; 
//画矩形 
g.drawRect(x,y,rectWidth,rectHeight); 
for(int i = 1;i<LABELS.length;i++){ 
g.drawLine(x,y+preferHeight*i,x+rectWidth,y+preferHeight*i); 
} 
//画菜单选项，并根据selected的值判断焦点 
for(int j = 0;j<LABELS.length;j++){ 
if(selected == j){ 
g.setColor(0x6699cc); 
g.fillRect(x+1,y+j*preferHeight+1,rectWidth-1,preferHeight-1); 
g.setColor(color); 
} 
g.drawString(LABELS[j],x+8,y+j*preferHeight+4,Graphics.LEFT|Graphics.TOP); 
} 
} 
public void keyPressed(int keyCode){ 
//根据用户输入更新selected的值，并重新绘制屏幕 
int action = this.getGameAction(keyCode); 
switch(action){ 
case Canvas.FIRE: 
printLabel(selected); 
break; 
case Canvas.DOWN: 
selected = (selected+1)%4; 
break; 
case Canvas.UP:{ 
if(--selected < 0){ 
selected+=4; 
} 
break; 
} 
default: 
break; 
} 
repaint(); 
serviceRepaints(); 
} 
//showNotify()在paint()之前被调用 
public void showNotify(){ 
System.out.println("showNotify() is called"); 
} 
private void printLabel(int selected){ 
System.out.println(LABELS[selected]); 
} 
}